This invention is concerned with making non-cellular dressings i.e. dressings for surgical or medical treatment of the human or animal body.
It has been proposed to employ two-part curable organosiloxane compositions for preparation of dressings. For example G.B. patent specification No. 1 492 581 describes dressings for open granulating wounds made by a process in which the two parts of a composition are mixed and then poured into an open wound where the composition cures to provide an elastomeric dressing. Compositions proposed for making such dressings have comprised poly(dimethylsiloxane) and finely divided filler base or "part A", and a catalyst part or "part B" comprising catalyst material for promoting room temperature curing and foaming of the composition according to the scheme .tbd.SiOH+HSi.tbd..fwdarw..tbd.Si--O--Si.tbd.+H.sub.2. By use of these compositions one may provide comfortable, non-adherent dressings conforming to the contours of the wound which are inter alia soft, resilient, permeable to air and somewhat absorbent.
Such a procedure for producing dressings leads to a variety of advantages related to improved patient comfort e.g. resulting from the non-adherent characteristics of the dressing and reduced care from nursing staff e.g. due to the increased possibility for the patient to remove the dressing to permit washing and/or disinfecting of the wound and dressing, followed by replacement of the dressing.
The correct use of two component compositions entails correct proportioning of the components and adequate mixing thereof. Adequate mixing of components of different viscosities can prove tedious when manual methods are used, but in general hand mixing of two part compositions or their component parts may be carried out by use of a suitable stirring implement, for example, a spatula. However, apart from the tedium involved, such mixing may lead to entrapment of air bubbles in the compositions. Particularly in those cases where more viscous compositions or faster curing compositions are used, these bubbles may become trapped in the composition as it cures. Entrapped bubbles in dressings produced render the dressings non-uniform and thus of variable quality. This is generally undesirable and in some cases may be wholly unacceptable. In addition, exposure of the composition to the environment during mixing to produce dressings is undesirable as it may be unhygienic in view of the possibility of contaminating the dressing as it is produced.
Apart from the desirability of mixing together the components without exposure to the atmosphere, those compositions which have been proposed for use in accordance with G.B. Pat. No. 1 492 581 tend to require separate mixing of the part A prior to admixture of the parts A and B. In the proposed compositions separation of the filler from the other components may occur.
Thus, the step of mixing the part A of the composition just prior to use is a critical step. When this step, or the proportioning of ingredients is not carried out adequately or at all (as may happen in practice), poor quality dressings result. It is troublesome to rectify improper mixing of such compositions because very often the fact of improper mixing is not recognized until after the supposedly curing composition has been applied to its allotted position. After recognition of failure to provide a suitably cured mass it becomes desirable to remove the defective material, clean up the site and to achieve the desired result by correct application or by some other practice. Such remedial operations are troublesome and inconvenient and are especially so in those cases where the product is used to provide a treatment for an open wound for example on the human body.
It is common practice to package materials in so-called aerosol form, particularly for surface coating applications. Materials which are usually packaged in this way consist primarily of liquids or solutions of comparatively low viscosity and which essentially do not require mixing with another ingredient prior to ejection from the package. Proposals have been made to extend the use of aerosol type packaging to curable two-part compositions. For example in G.B. specification No. 861 448 there is described and claimed a package comprising a pressure tight container having a closeable outlet orifice and containing a polymerizable material of such a nature that it will convert at a temperature below approximately 150.degree. F. (b 65.degree. C.) rapidly and completely to an organic polymer only when released from said outlet orifice, and a propellant that is gaseous at room temperature and pressure, said propellant being present in a sufficient quantity and being capable of exerting a sufficient pressure within the container to expel said polymerizable material through said orifice. In a preferred form of construction, an agent for activating polymerization is maintained with a volatile propellant physically separated from the polymerizable material in a compartment from which it may be expelled through an orifice into a mixing chamber wherein said polymerizable material and said activator are blended under reduced pressure prior to being expelled to the atmosphere.
The applicant has found it impossible satisfactorily to package certain curable polysiloxane compositions using known aerosol type packages. There exists a particular problem of packaging filled materials which have a consistency which is thicker than the liquid polysiloxane fluids and these materials are among those which are particularly beneficial for the production of dressings.